The present invention relates to a dynamometric screw-driver comprising a friction torque limiter and more particularly a torque limiter having a torsion spring of the type disclosed in FR-A-2 250 403, i.e. a torque limiter comprising a helical friction band coupled at both ends to a torsion spring which is coaxial therewith. This torque limiter is mounted inside the tubular handle of the screw-driver between two axial abutments so that the torsion spring applies the helical band against the inner surface of the handle. Further, the helical band and the torsion spring are connected at one of their coupled ends to the stem of the tool.
Screw-drivers of this type are particularly reliable since their torque limiter ensures both the stability of the sliding torque upon rotation in the screwing direction and an absence of sliding upon rotation in the unscrewing direction. Further, the sliding torque is insensitive to variations in the coefficient of friction. A serious problem is however presented by the adjustment of the sliding torque of the torque limiter. Indeed, this adjustment requires the adjustment of the torsion of the spring which can only be achieved by exterior means, the same being true in respect of the measurement of the torque obtained.
Now, a dynamometric screw-driver is a hand tool which must be capable of being conveniently adjusted at any moment by the user with no accessory tooling or auxiliary measuring bench.